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If I remember correctly, this is the scene where Blanc interviews every member of the family, which serves both as a general introduction for the viewer and the start of the investigation.

During each interview, Blanc was trying to get the suspects to reveal hints and suspicions, and I think that's what he's doing here: by trying to depict Walt in a more positive light than Linda, he may want to trigger her into badmouthing Walt, potentially revealing a motive for the murder.